Along with digitization of information, it has become more easy to share and use information over a broad range. Then again, it is very important to manage digital documents and documents obtained by printing the digital documents.
Japanese Patent Application No. 10-319611 (corresponding to Japanese Patent Laid-Open No. 2000-151581) discloses a technique for collecting documents based on barcodes printed on documents. Also, Japanese Patent Application No. 6-170584 (corresponding to Japanese Patent Laid-Open No. 8-36564) discloses a system that pertains to distribution and collection of digital documents.
The aforementioned techniques append barcodes or the like indicating the locations of original digital documents to printed documents so as to detect original digital documents. However, if such barcodes are damaged or contaminated, original digital documents can no longer be detected. Since printed documents and original digital documents are not simultaneously managed, if documents are discarded, printed documents must be collected and discarded, and original digital documents must be separately erased. This discard job is very complicated in terms of management, and secret information which remains stored in a storage device may leak if original digital documents are forgotten to be erased.